Process for producing textured coatings

ABSTRACT

In a process for curing a coating on a substrate, which coating has a thickness of about 0.1 mil to about 10 mils, with ultraviolet light comprising the following steps; 
     (a) applying a coating, which is curable with ultraviolet light, to the substrate, said coating having a viscosity, as applied, of at least about 50 centipoises; 
     (b) exposing the coated substrate to ultraviolet light having wavelengths in the range of about 1800 Angstroms to about 2750 Angstroms in an inert atmosphere for a period of time sufficient to initiate texturing at the surface of the coating; 
     (c) maintaining the coated substrate from step (b) in a space essentially devoid of ultraviolet light for a period of time sufficient for the surface of the coating to texture; and 
     (d) exposing the coated substrate from step (c) to ultraviolet light having wavelengths in the range of about 1800 to about 4000 Angstroms in an inert atmosphere or air until the coating is essentially cured, 
     the improvement comprising, after step (a) and prior to step (b), increasing the viscosity of the coating by exposing the coating to ultraviolet light, said viscosity being increased to a viscosity no higher than that at which the coating is capable of being textured in steps (b) and (c), above.

TECHNICAL FIELD

This invention relates to a process for providing a textured andphotocured coating on a substrate.

BACKGROUND ART

It is well known in the photocure art to provide various finishes forsubstrate coatings such as flat, glossy, or wrinkle finishes, orintermediate variations of these finishes. These finishes have, up tothe present, been attained by using particular chemical formulations oradditives such as flatting pigments; allowing a time interval betweenexposures to ultraviolet light; curing all of the coating, but thesurface, and then subjecting the coated substrate to ultravioletradiation in air until the surface is fully cured; with ultravioletlight, first obtaining a partial cure in air of the interior andexterior coating, the former to a greater degree, second, curing theexterior more than the interior, and finally curing the interior; curingin air all of the coating except for its surface and then irradiating inan inert atmosphere; and curing first the interior of the coating andthen the exterior at particular irradiation levels.

The textured finish is of concern here. The term "textured" is definedas a woven or interwoven appearance characterized by the number ofweaves or strands per unit of linear distance. This finish is producedby providing a time interval between exposures to ultraviolet light.Unfortunately, this process as it is presently practiced is limited withrespect to its capability of (i) providing different texture densitiesusing the same coating, i.e., the provision of a controlled range oftexture densities running from coarse to fine to very fine to ultra-fineto texture free; (ii) yielding what is considered to be an ultra-finetexture ("ultra-fine texture" is defined as greater than 150 weaves orstrands per inch.); (iii) providing improved optical clarity,non-burnishing properties, and rheology; and (iv) providing selectiveand/or differential texturing.

More specifically, the known texturing process utilizes very thincoatings to achieve sufficient control over the process to provide thedesired texture pattern and depth. The disadvantage of the thin coatingis that any imperfection in the coating, such as the pressure of foreignmatter, shows up at the surface resulting in a substantial waste factor.Further, where thin coatings are not used, the typical result is arelatively coarse and deep texture, i.e., relatively fine textures aresimply not obtainable with thick coatings using known texturingtechniques.

DISCLOSURE OF THE INVENTION

An object of the invention, therefore, is to provide a process for theproduction of textured coatings wherein the texture density iscontrolled, ultra-fine, and selective; the coating has desirable opticalclarity, non-burnishing, and rheological properties without theutilization of additives; the texture density is independent of coatingthickness; and the texture is relatively fine as opposed to coarse.

Other objects and advantages will become apparent hereafter.

According to the present invention, an improvement has been discoveredin the known process for curing a coating on a substrate, which coatinghas a thickness of about 0.1 mil to about 10 mils, with ultravioletlight comprising the following steps:

(a) applying a coating, which is curable with ultraviolet light, to thesubstrate, said coating having a viscosity, as applied, of at leastabout 50 centipoises;

(b) exposing the coated substrate to ultraviolet light havingwavelengths in the range of about 1800 Angstroms to about 2750 Angstromsin an inert atmosphere for a period of time sufficient to initiatetexturing at the surface of the coating;

(c) maintaining the coated substrate from step (b) in a spaceessentially devoid of ultraviolet light for a period of time sufficientfor the surface of the coating to texture; and

(d) exposing the coated substrate from step (c) to ultraviolet lighthaving wavelengths in the range of about 1800 to about 4000 Angstroms inan inert atmosphere or air until the coating is essentially cured.

The improvement comprises, after step (a) and prior to step (b),increasing the viscosity of the coating by exposing the coating toultraviolet light, said viscosity being increased to a viscosity nohigher than that at which the coating is capable of being textured insteps (b) and (c), above.

DETAILED DESCRIPTION

Apparatus that can be used to carry out the process is similar to thatdisclosed in U.S. Pat. No. 3,807,052, which is incorporated by referenceherein. In '052, apparatus for carrying out the curing of coating onsubstrates with ultraviolet mercury lamps is described using theprinciple of laminar flow inerting by which curing is enhanced throughthe replacement of oxygen on the surface of a moving coated substratewith an inert gas atmosphere, usually nitrogen. The particular apparatusdescribed is eminently satisfactory for step (d) recognizing that insubject process, however, air can be substituted for the inert gas of'052. The steps preceding step (d) are carried out by merely modifyingthe apparatus to accommodate the viscosity increasing step and steps (b)and (c). This simply means adding two banks of ultraviolet mercury lampsand a gap or dark space to the front of the '052 apparatus. The overallconstruction of the structure remains the same, however, insofar as theconveyer belt, gas injection means (where desired), and the body of theapparatus is concerned.

A typical apparatus configuration is 76 inches long operating at 20 feetper minute. The viscosity increasing step is conducted in the first teninch portion. Step (b) is conducted in the latter half of the nexttwenty-five inch section. The next twenty-four inch portion is wherestep (c) is accomplished. This is also where the gas injection meansresides. Finally part of step (d), i.e., partial curing, is carried outin the next five inch section. The function of the last twelve inches isto serve as an exit tunnel for inerting and as a light shield. Step (d)may be completed in any one of a number of converted follow-onultraviolet curing units. The aforementioned configuration isparticularly advantageous for those who already possess curing units. Inthe event that a new fully integrated unit is desired, the five inchportion is extended to about 72 inches so that curing can be completedin the same unit.

Another typical configuration is seventy-eight inches in length whereinthe viscosity increasing step is carried out in the first sixteen inchpart. There is then a six inch gap followed by a ten inch portion inwhich nitrogen is dispensed from the gas injection means. Step (b) isthen carried out in the next six inch section; step (c) in the nexttwelve inch section; step (d) in a five inch section followed by atwenty-three inch section in which the process is terminated.Alternatively, twenty-three inches is devoted to step (c) andtermination takes place in the last twelve inches. It will be understoodthat the length of the step (c) section can be varied and thetermination section is also varied accordingly, a longer step (c)section meaning a shorter termination section and the converse. Varyingthe step (c) or dark space section provides added control for theprocess and a section where compensation can be made for line speedvariations.

An improved arrangement adds 12 to 24 inches to the system and providesan air venturi injection means prior to the viscosity increasingsection. This is followed by a variable flow air inlet, which reducesthe inerting level in the viscosity increasing section. The air isinjected perpendicular to the belt and is controlled by a variable inletdamper. The next section is devoted to step (b) after which comes thenitrogen injection means doubling as the step (c) section. The lastsection is the step (d) section where the process terminates in a fullcure.

Advantageous configurations for the variable flow air inlet, whichfollows the viscosity increasing section, are as follows: where thecoated substrate has been fully inerted, the entrance to the air inletis closed and sealed; where the coated substrate is permitted to enterwith air, an upstream air inlet door is opened to permit the entry ofair and a downstream door is opened to permit the exit of downstreamnitrogen together with the air. In this way air is drawn to the surfaceof the coated substrate at the beginning of the air inlet section andthe downstream nitrogen strips the air in preparation for step (b) inthe latter half of the air inlet section. The entire air inlet sectionis typically about six inches in length.

Typical belt speeds are in the range of about 20 feet per minute toabout 120 feet per minute and are preferably about 60 feet per minute toabout 80 feet per minute. Air injection, where used, is typically in therange of 100 standard cubic feet per hour per foot of line width toabout 400 standard cubic feet per hour per foot of line width and ispreferably in the range of about 150 standard cubic feet per hour perfoot of line width to about 300 standard cubic feet per hour per foot ofline width. Nitrogen (or other inert gas) injection, again where used,is typically in the range of about 50 standard cubic feet per hour perfoot of line width to about 650 standard cubic feet per hour per foot ofline width. Gas injection, of course, is coordinated with belt speed inorder to provide the desired result. Coordination is accomplished bymanually adjusting the flow upward as the belt speed is increased. Step(b) is always accompanied by inerting while the viscosity increasingstep and steps (c) and (d) can be carried out in air or in an inertatmosphere.

In the viscosity increasing step, the ultraviolet light that is used toachieve the increase in viscosity can have wavelengths in the range ofabout 1800 to about 4000 Angstroms. The ultraviolet light may beprovided by full spectrum mercury lamps, spectrally controlled mercurylamps, black lights, or "L" germicidal lamps.

According to The Condensed Chemical Dictionary, 6th Edition, Rose,Reinhold Publ. Corp., 1961, "ultraviolet" is defined as the "region ofthe electromagnetic spectrum including wave lengths from 100 to 3900 A .. . ". Since some definitions expand the range to about 4100 Angstroms,it is understood that "about 4000 Angstroms" is considered here toinclude this expanded range up to 4100 Angstroms.

The principal source of ultraviolet light or radiation insofar asphotocuring is concerned is the medium pressure mercury lamp referredto, for example, in U.S. Pat. No. 3,983,385, also incorporated byreference herein. Typically, such a lamp is made up of a fused quartzenvelope or tube sealed at each end. Inside the tube at each of theseends is a tungsten electrode connected to a power conducting wirethrough an intermediate molybdenum strip, the strip being embedded inthe quartz to provide what may be called a quartz to metal seal. Thelamp is filled with argon gas and a small amount of mercury prior tosealing. The amount of gas in the tube is such that the internalpressure will be approximately one atmosphere at an operatingtemperature, which is about 800° C. to 1000° C. The amount of mercury ina full spectrum lamp is such that the full spectrum of ultravioletlight, i.e., all the wavelengths which mercury is capable of radiating,emanates from the tube when energized provided that the quartzcomposition of the tube has a transmittance of 100 percent with respectto those wave lengths. To obtain the wavelengths required or preferredin this invention, the composition of the quartz is either altered by,for example, doping or a filter, in the form of a Vycor glass jacket orplate, is placed in between the lamp and the surface to be cured. Boththe quartz and the Vycor glass filter can be made up, and this isconventional, to provide the desired transmittance, e.g., one whichfilters out essentially all of the wavelengths below about 3000Angstroms. A commercial designation of such a lamp is Voltarc H 22C/24 V17. Another type of lamp or lamp/filter combination removes essentiallyall of the radiation below about 2000 Angstroms and reduces thetransmittance of radiation between about 2000 Angstroms and 2550Angstroms by at least about 50 percent. This particular lamp isgenerally known as an "ozone-free" or spectrally controlled lamp. It ismade of quartz doped with titanium dioxide and it transmits theultraviolet light as follows:

    ______________________________________                                        wavelength                                                                    (Angstroms)       percent transmittance                                       ______________________________________                                        less than 2000    essentially zero                                            2000 to 2550      less than 25                                                2550 to 3000      greater than 50 to 75                                       greater than 3000 essentially 100                                             ______________________________________                                    

A commercial designation for the "ozone-free" or spectrally controlledlamp is Voltarc H22C/24 G,(SC-1).

Curing, such as that referred to in step (d), takes place in ultravioletlight having wavelengths in the range of about 1800 to about 4000Angstroms and preferably about 2000 to about 4000 Angstroms. The morepreferred wavelengths are in the range of about 2500 to about 4000Angstroms. An alternative, but a compromise, would be to cure withultraviolet light having wavelengths in the range of about 2000 to about4000 Angstroms with the provision that at least about 50 percent of theultraviolet light in the range of about 2000 to about 2500 Angstroms isfiltered out.

An example of a full spectrum mercury lamp is a Voltarc H22C/24B. Anexample of a spectrally controlled lamp is a 2000 to 4000 Angstromultraviolet lamp with variable input power of 25 to 75 watts per linearinch of lamp length. An example of black lights is an array oftwenty-four lamps of 3000 to 4000 Angstroms with an input of 1 to 2watts per linear inch. An example of the "L" type germicidal lamp is a2537 Angstrom ultraviolet lamp without ozone production. The blacklights can be mixed with the "L" type germicidals, e.g., in thetwenty-four lamp black lights array, twelve "L" type germicidals can besubstituted for twelve black lights. Preferably, the germicidals precedethe black lights in the array. In is noted that the viscosity increasinglamp, when operated in air, will generally require more power input fromthe ultraviolet lamps assigned to it than the power input to step (b),i.e., more lamps and/or more powerful lamps.

Typical exposure times in the viscosity increasing section are in therange of about 0.5 to about 50 seconds and are preferably about 1.5 toabout 30 seconds. Any increase in viscosity during the viscosityincreasing step up to the point at which the coating is capable oftexturing in steps (b) and (c) will provide the controlled texturingsought for by subject process.

A test to determine whether the viscosity has been increased to itslimit, i.e., the viscosity above which texturing as per steps (b) and(c) will not take palce, is called the Diffraction Test.

The "Diffraction Test" is carried out in accordance with the followingsteps:

1. select an ultraviolet light curable composition;

2. remove any additives, which would render the composition (in thecured state) opaque to all colors of the visible white light spectrum;

3. coat the composition (modified as per step 2, if necessary) onto aclear, i.e., transparent, substrate such as glass;

4. increase the viscosity of the coating by exposing the coatedsubstrate to ultraviolet light having wavelengths in the range of about1800 to about 4000 Angstroms.

5. after the viscosity is increased, texture the coating using steps (b)through (d) set forth above;

6. the coated substrate is then held up at arm's length between the eyeof the operator towards a single incandescent 100 watt tungsten bulb(bulbs of various sizes can be used, e.g., 75 to 150 watt bulbs) about25 to about 50 feet away so that the operator can see the bulb throughthe transparent coating and substrate. The bulb can be white, frosted,or clear. The coating passes the Diffraction Test if the operator isable to see a cicrular rainbow concentric to the white light source. Theobject here is to focus on a point white light source. The more intensethe light source, the greater the distance that can be permitted betweenthe transparent coating and substrate and the source and, conversely,the less intense the source, the shorter the distance between thetransparent coating and substrate and the source. The eye is always keptat about arm's length from the coated substrate. As long as the lightsource is white and provides a point of light to focus on, any type oflight can be used, e.g., incandescent or fluorescent. The circularrainbow is made up of concentric bands or rings of color progressingfrom blue on the inside of the circle closest to the point of light tored on the outside of the circle farthest from the point of light. Thesecolor bands indicate that the viscosity level is not too high for atexture pattern to be produced. It should be noted that a transparentpigment present in the coating composition could serve to mask out theband or ring corresponding to the color of the pigment.

A rough test to determine whether the viscosity has been increased aboveits limit is based on whether or not the coating has been cured duringthe viscosity increasing step. If the coating has not been cured, itwill be readily dissolved by acetone, lacquer thinner, or a similarsolvent. If, on the other hand, it has been cured, the coating willsurvive the rub test, which consists of rubbing the surface of thecoating with a cloth saturated with one of the mentioned solvents. Ifthe coating is cured, it will survive vigorous rubbing. The initialviscosity of the coating, as applied, is no different from that at whichit is conventionally applied under ambient conditions. Typical viscosityranges for various coating techniques are as follows:

    ______________________________________                                        Means of        viscosity range                                               applying coating                                                                              (in centipoises)                                              ______________________________________                                        gravure          50 to 200                                                    roller          150 to 500                                                    flow            400 to 1500                                                   screen          750 to 5000                                                   litho             5000 to 10,000                                              ______________________________________                                    

Generally, of the foregoing, the gravure and litho coatings are theleast desirable for subject process.

The increase in viscosity must take place in situ, i.e., after thecoating has been applied to the substrate. While infrared energy may beused to further control the viscosity, step (b) is preferably initiatedimmediately after the viscosity change has been essentially completed. Asubstantial increase in viscosity, i.e., at least about 25 percent, isgenerally used to obtain the desired effect. The viscosity is notnecessarily uniform throughout the coating, but can vary from top tobottom depending on the wavelength range of the ultraviolet light usedin the viscosity increasing step. The substitution of a higher viscositycoating in lieu of the viscosity increasing step or the use of additivesto increase the viscosity is not acceptable. The increase in viscositymust be accomplished by means of ultraviolet light. This is describedelsewhere in the specification.

Step (b), the step in which texturing (or shrinkage) is initiated, usesultraviolet lamps having wavelengths in the range of about 1800 to about2750 Angstroms, and preferably in the range of about 1849 to about 2537Angstroms. These wavelengths may be achieved by using the full spectrummercury lamps mentioned above in connection with the viscosityincreasing step; however, a more practical lamp is a germicidal lamphaving a typical power input per lamp of about one watt per linear inch.The number of lamps needed here will vary according to line speed, thelength of the step (b) section, the exposure time, and the size of thelamp array.

Step (c) is usually accomplished by providing a space devoid ofultraviolet light which may be referred to as a dark space. The lengthof a typical dark space would be twenty-four inches in the 20 to 150feet per minute range. Other typical space lengths are noted above. Thisis the place where texturing of the surface proceeds to completion afterit is initiated in step (b).

Step (d), is accomplished by using ultraviolet lights having wavelengthsin the range of about 1800 Angstroms to about 4000 Angstroms andpreferably in the range of about 2000 Angstroms to about 4000 Angstromsto cure the coating. The cure is essentially completed in this step andcannot be reversed. Spectrally controlled or full spectrum ultravioletmercury lamps generating 100 to 200 watts per linear inch are typical ofthe lamps used to perform this step.

The coatings used are conventional photocurable coatings. They areuseful in subject process if they will texture after being put throughsteps 1, 2, 3 and 5 of the Diffraction Test. Note that it is notnecessary to increase the viscosity to make this determination. Thistexturing test is especially advantageous in view of the fact that manycoatings are proprietary to the manufacturer and thus the chemicals usedin the coating are not disclosed to the public.

Some coatings which find utility here are found in U.S. Pat. No.3,840,448, incorporated by reference herein. Other coatings (both clearsand colors) may be found among the conventional ultraviolet lightcurable (polymerizable)graphic art screen ink compositions. Typically,these screen inks contain one or more of ultraviolet light polymerizablemonomers; ultraviolet light polymerizable oligomers; ultraviolet lightreactive crosslinking agents; pigments; flow agents; leveling agents;adhesion promotion agents; and ultraviolet light sensitizing agents.Their pigment content is relatively low when compared with lithographicinks, i.e., about 5 percent by weight for screen inks against about 40percent by weight for lithographic inks.

The components which make up conventional ultraviolet lightpolymerizable graphic art screen ink compositions are, except for thepigments, generally reactive in the curing environment. The oligomersand monomers typically make up about half of the composition by weight;the adhesion promoter about 15 to 20 percent by weight; the crosslinkingagent about 10 to 15 percent by weight; the flow agent or viscosityreducing agent about 5 to 10 percent by weight; and pigments,sensitizing agents, and leveling agents, each about 5 percent by weight.

The oligomers are often acrylate terminated urethanes formed from, forexample, the reaction of an aliphatic diisocyanate, a polyester polyol,and hydroxyethylacrylate or toluene diisocyanate, acrylic acid, andpenaterythritol. The monomers can be any one of the oligomer reactants,but are usually acrylates. These oligomers and/or monomers usually servein a diluent capacity in addition to their function as the main part ofthe ultimate coating. The crosslinking agents are polyfunctional such asneopentyl glycol diacrylate. Other crosslinking agents may be found inU.S. Pat. No. 4,003,751 at column 6, lines 41 to 58, incorporated byreference herein. The ultraviolet light sensitizing agents orphotoinitiators are preferably two part compositions, one of thephotoinitiators being receptive to those wavelengths which provide athrough-cure and the other, to those which provide a surface cure. Anexample of the surface cure sensitizing agent is dimethoxy phenylacetophenone and of the through-cure agent, benzophenone. A number ofphotoinitiators as well as monomeric diluents and leveling agents may befound in U.S. Pat. No. 4,003,877, at column 4, line 50, to column 5,line 58, and column 6, line 67, to column 7, line 9, all incorporated byreference herein. Another list of photosensitizers may be found in U.S.Pat. No. 3,847,767, column 3, lines 48 to 70, which is also incorporatedby reference herein. Acrylic monomers, photosensitizers, andcrosslinking agents may be found in U.S. Pat. No. 4,023,973 at column 4,line 1, to column 5, line 63, incorporated by reference herein. A listof suitable pigments may be found in U.S. Pat. No. 3,803,109 at column9, lines 54 to 64, incorporated by reference herein. Screen inkformulations may be found in U.S. Pat. No. 3,803,109, example 7, and "UV Curing: Science and Technology," edited by S. Pappas, TechnologyMarketing Corporation, 1978, page 201, both incorporated by referenceherein. Adhesion promoters compatible with the substrate are often used,e.g., vinyl acetate resin for a vinyl substrate. A useful screen inkformulation may be prepared by first grinding UVIMER DV-775 acrylateterminated urethane oligomer 12.2 parts (by weight); DT-790 red pigment3.0 parts; and 13-7000 red pigment 0.9 parts and adding to the followingmixture which is first ground: UVIMER DV-775 acrylate terminatedurethane oligomer 20.0 parts; UVIMER DV-530 acrylate terminated oligomer5.0 parts; vinyl acetate resin adhesion promoter 14.0 parts; n-vinylpyrollidone flow agent (viscosity reducer) 7.0 parts; neopentyl glycoldiacrylate crosslinker 10.0 parts; dimethoxy phenyl acetophenonephotoinitiator 5.0 parts; and benzophenone photoinitiator 2.0 parts. Thefirst mixture is called the grind portion and the second, the let-downportion.

Other useful oligomers and monomers may be found in U.S. Pat. Nos.3,661,614; 3,825,479; 4,026,939; 4,056,453; and 4,082,710, allincorporated by reference herein.

The compositions of various other conventional and useful coatings areproprietary to the manufacturer. Their label designations andmanufacturer's name are as follows, however:

I. UV 30-99 Graphic O.P. Clear Ink with about 20 percent UV 30-98viscosity modifier from Colonial Printing Ink Co., East Rutherford, N.J.

II. DURACOTE floor coating from Armstrong World Industries, Lancaster,Pa.

III. Naz Flex UV-170 O.P. Clear from Naz Dar Company, Chicago, Ill.

IV. V-1509 Flatted Clear from Polychrome Printing Ink Division,Cincinatti, Oh.

V. PSG-27 O.P. Clear from Kansas City Coatings, Inc., Kansas City, Mo.

VI GA-72 Flatted Clear from Dynachem Corp., Tustin, Calif.

VII. UV 580-293 Litho O.P. Clear from Colonial Printing Ink Co. (see Iabove).

VIII. UV 703 from Polychrome (see IV above).

IX. PSG PB-18 Tsp. Red Ink from Kansas City Coatings (see V above).

X. UV 21033 Flatted Clear fom Polychrome (see IV above).

XI. UV 580-290 Litho Overprint Clear from Colonial Printing Ink (see Iabove).

XII. RC-001 Clear from H. B. Fuller, Minneapolis, Minn.

XIII. V1503 Overprint Clear from Polychrome (see IV above).

XIV. 701 from Polychrome (see IV above).

It should be pointed out here that Syloid silcia gels and other flattingagents are not needed in the coating compositions useful in subjectprocess and, in general, have been found undesirable. Further, theprocess is generally non-burnishing simply because pigments, fillers,and the like are not used to any meaningful extent.

The substrates upon which the coatings are applied are also coventional,e.g., vinyl plastics, both flexible and rigid, the flexible vinyl beingsupported or unsupported; nylon plastics; paper; paper board; glass;pressboard; brushed aluminum; and any stock with characteristics similarto the foregoing. Other examples of substrates are Lexan thermoplasticcarbonate-linked polymers (hereinafter Lexan polymer) produced byreacting Bisphenol A and phosgene; litho stock; various metals or metalalloys in addition to brushed aluminum, mentioned above, usually insheet form; polyester plastics and various plastic flooring materialssuch as vinyl tile, vinyl-asbestos tile, and foamed back sheet goods.The thicknesses of these substrates is generally in the range of about0.5 mil to about 1000 mils and is preferably in the range of about 5mils to about 250 mils.

Subject process can be used to manufacture numerous products, e.g.,nameplates, faceplates, LED and LCD readout display covers, signaturestrips for credit cards, floor tiles and floor sheet goods, post cards,greeting cards, non-gloss picture covers, magazine centerfolds, coatingsfor pictures and art works, poster coatings, non-glare covers for TVtubes and display screens, diffraction sheets for color separation,advertisement copy readability enhancement, replacement for non-glareglass or plastics, low gloss coatings for vinyl products such as wallcoverings, low gloss coatings for wood or imitation wood products suchas panels, furniture, counter tops, controlled gloss top coats forcabinet tops and other work surfaces, low gloss clear coatings forplastic and paper playing cards, low gloss clear coatings for testpatterns, non-gloss separators for photo albums, low gloss visibilityenhancement coatings for signs, license plates, emblems, and low glosswith improved optical clarity applications.

Step (a) considers the application of the coating to the substrate andthis can be accomplished in many ways, all conventional. For example,the inks may be applied through a screen. Screens of 200, 350 and 420mesh (threads per linear inch) are commonly used. Other usefultechniques for applying coatings to substrates are roll coating, flow orcurtain coating, gravure and litho.

After step (a), the viscosity increasing step is carried out. This stepis preferably carried out in the presence of air although inert gasescan be used. As noted above, any increase in the viscosity of thecoating between step (a) and (b) will provide improved and controlledtexturing. Any point from a slight increase to a point where thetextured coating is still capable of passing the Diffraction Test can beselected. It will be understood that a careful record of the compositionand process parameters must be kept so that the same texture can beobtained at any time. In this respect, it is beneficial to have as manyconstants as possible when embarking on a program for seeking desirabletextures for a particular utility, e.g., by using the same apparatus,including UV spectrum, watts per linear inch, UV flux, atmosphere,standard cubic feet per hour flow rates and line speed or belt speed.

One of the characteristics of the coating after it has gone through theincrease in viscosity is that the procedure is substantially reversible,e.g., the application of infrared energy will bring the coating backtowards its initial viscosity. The infrared energy can, in addition, beused for fine control of the degree of viscosity. Calrod heating unitshaving 50 watts per linear inch input (i.e., per inch of substratewidth) are useful for this technique, which also allows for selectivevariation of the texture pattern over dark vs. light colored substrateareas.

The viscosity increasing step can be carried out with variousultraviolet lamps, some of which were mentioned above. Examples of otherultraviolet lamps and the number of lamps used are as follows: six blacklight ultraviolet lamps, each providing wavelengths in the 3000 to 4000Angstrom range (1 to 2 watts input per linear inch); combination of theblack lights previously mentioned and 2537 Angstrom "L" typegermicidals; spectrally controlled 2000 to 4000 Angstrom ultravioletlamp with variable input power and delivering 25 to 75 watts per linearinch; a 100 watt per linear inch input spectrally controlled ultravioletlamp operated at about 64 watts per linear inch (1180 volts A.C. and 1.3amperes A.C.) and at about 54 watts per linear inch (1200 watts A.C. and1.1 amperes A.C.), delivering about 2000 to 4000 Angstroms, and Vycorenvelope ultraviolet lamp, 3000 to 4000 Angstroms output, operated at aninput power of 64 watts per linear inch. The choice of spectralwavelength in the viscosity increasing step (2000 to 4000 Angstroms asagainst 3000 to 4000 Angstroms) can be very significant with respect tothe type of texture achieved (direction of texture growth) and the needfor an infrared module for fine viscosity control. In a 2000 to 4000Angstrom unit, an infrared module can be used to reduce the viscosity ofthe coating over the dark background areas and keep the viscosity atsubstantially the same level over the light colored background areas.Thus, the dark areas can be made to texture while the light areas remainglossy and/or have an ultra-fine texture pattern. In a 3000 to 4000Angstrom unit, the presence of only long ultraviolet wavelengths allowsthe wavelengths to pass through a clear coating and either be absorbedor reflected from the substrate surface and/or a reflective ornon-reflective back-up material in the case of a transparent substrate.The reflected ultraviolet light increases the viscosity level in thereflective areas as against the dark areas providing a decrease intexture over the reflective areas and a relatively greater amount oftexture in the non-reflective areas.

It has been demonstrated that in the viscosity increasing step, thelayers of the coating are only partially cured (substantiallyreversible) and tend to remain in a semi-liquid state. The partial cureof the lower layer is demonstrated by the fact that the textured patternhas a tendency to grow downward from the surface of the coating when2000 to 4000 Angstroms ultraviolet lamps are used in the viscosityincreasing step, i.e., the textured pattern is depressed below thecoating surface. With 3000 to 4000 Angstrom ultraviolet lamps used inthe viscosity increasing step, the texture pattern has a tendency togrow upward from the coating surface, i.e., the textured pattern israised above the surface. These same 3000 to 4000 Angstrom lamps givethe texture more sensitivity to background colors such that coarsetextures are produced over dark or non-reflective colors and ultra-fineor glossy textures over light or reflective colors. The 2000 to 4000Angstrom ultraviolet lamps, on the other hand, give the texturing lesssensitivity to background or substrate colors. In this case, about thesame texture can be achieved over both dark or non-reflective and lightor reflective areas.

We have discussed texturing control in terms of the viscosity increasingstep. It should be remembered, nowever, that the actual texturing is notinitiated until step (b) and is not completed until step (c). Thus, whatis done in the viscosity increasing step has a profound effect on thebalance of the process.

The resulting textures can be so fine as to be visible only under highmagnification. In fact, texture weaves or strands about one fifth to onetenth of the size of an about 150 line screen lithodot (1.3×10⁻³ to6.7×10⁻⁴ inch) have been observed. In addition to the fineness of thetexture, extremely uniform textures are achieved even under the poorestof conditions, e.g., when poor screen draw-downs are textured.Variations in viscosity in the viscosity increasing step are observed toaffect the fineness of the textured pattern. Fine textures arecharacterized by a low gloss surface; very fine textures by a mediumgloss surface; and ultra-fine textures by a semi-gloss surface.

Simply because of logistics, there is generally a brief delay betweenthe viscosity increasing step and step (b). There is no indication thatany delay is required for the process to function properly. Because ofphysical constraints, there, of course, must be a delay when an infraredmodule is interjected between the viscosity increasing module and thetexturing module (step (b)). In any case, it is preferred that thedistance between the viscosity increasing module and the textureinitiating module (step b) be as short as possible in order to avoid anyuncontrolled changes in viscosity.

Preferred conditions for the viscosity increasing step are as follows:

1. input power range, minimal, of ultraviolet lamp: about 30 to about 45watts per linear inch;

2. optics: prefocused elliptical optics;

3. spectrum: about 2000 Angstroms to about 4000 Angstroms where thethickness of the coating is equal to or less than 1.0 mil, nominal, andabout 3000 Angstroms to about 4000 Angstroms where the thickness of thecoating is greater than about 1.0 mil, nominal;

4. power supply: multiple lamp or single lamp supply depending upon thelength of the lamp;

5. cooling: convection and radiation only for improved lamp operationalstability;

6. substrate control: static hold-down may be used where feasible; and

7. flux: about 500 to about 1100 watts of ultraviolet light per squarefoot where prefocused and about 150 to about 300 watts per square footwhere interfocused.

Adjustment of the lamp output power, i.e., watts per linear inch, in theviscosity increasing step is used to achieve a wide range of texturesrunning from fine to ultra-fine. It is believed that the textue patternsproduced by subject process have densities of about 10,000 to about30,000 texture weaves or threads per linear inch when the DiffractionTest viscosity increase limit is reached. Generally, the texture patternyields a greater density of texture weaves or threads per inch as thenumber of ultraviolet lamps is increased. The depth of the texture may,however, be significantly reduced thereby and a more glossy surface mayresult.

Where the ratio of volume to surface (in the coating) is higher, thereis an indication that the input power range can be lowered in view ofthe reduced effects from oxygen inhibition. In any case, subject processis found to produce highly satisfactory textures with thick coatings.Conversely, high input power ranges are indicated for thinner coatings,which are subject to greater oxygen inhibition.

A three lamp viscosity increasing module has been developed to providesufficient flexibility for handling a full range of coatings which mightbe utilized in this process. Typically, the three lamps are in a lineabove and across (perpendicular to) the path of the coated substrates.Each lamp provides wavelengths in the 2000 Angstroms to 4000 Angstromspectrum with a input power range of 30 to 40 watts per linear inch.Each lamp is backed by a prefocused reflector, which can be verticallyadjusted to defocus, if required. Between each lamp and the coatedsubstrate a Vycor filter for the 3000 to 4000 Angstrom range is providedas required. The focal band (as observed) is about 0.5 inch and theultraviolet flux is about 800 to 1100 watts per square foot calculatedat 26 percent lamp efficiency. Differential or selective texturing,i.e., the ability to texture differentially or selectively over dark ornon-reflective and light or reflective backgrounds is successfullyaccomplished with the three lamp modules. These modules are particularlysuccessful when 2000 to 4000 Angstroms are used for coatings less than 1mil in thickness and 3000 to 4000 Angstroms for coatings 1 mil orgreater in thickness. First, the viscosity is raised to a point where notexturing is achieved over any background colors. Then the input poweris reduced or the line speed is increased until the viscosity is reducedto achieve the desired level of texturing over the dark ornon-reflective colors. Slight adjustments in viscosity are then made tofine tune the differential or selective texture contrast as desired. Asa general rule, fine control and uniformity of the textures of clears ontransparent substrates can be enhanced by backing the substrate witheither reflective or non-reflective materials during the viscosityincreasing step. This procedure can be used instead of changing theinput power energy or the line speed to achieve modest viscosity andsubsequent texture density changes.

The use of an air atmosphere in the viscosity increasing step cansometimes require a very large input power, thus introducing excessiveheat where heat sensitive substrates are concerned. Low power blacklights have been used to mitigate this problem with limited success inan air atmosphere. The effect of black lights, however, is greatlyenhanced if they are operated in an inert atmosphere, preferablynitrogen, and this technique is suggested.

After the viscosity increasing step is carried out, step (b) isproceeded with, i.e., the coated substrate from the viscosity increasingstep is exposed to ultraviolet light having wavelengths in the range ofabout 1800 Angstroms to about 2750 Angstroms preferably at 1849 and 2537Angstroms, in an inert atmosphere, preferably nitrogen, for a period oftime sufficient to initiate texturing (or shrinkage) at the surface ofthe coating. The resultant texture must normally be observed under 10 to50X magnification due to the extreme fineness of the texture weaves orthreads. The preferred spectrum for this step (b) is wavelengths atabout 1849 Angstroms and about 2537 Angstroms and typical timessufficient to initiate shrinkage are in the range of about 0.25 to about2.5 seconds. These times, of course, depend on the input power energy,the line speed, and the shrinkage factor of the specific coating used.Typical step (b) parameters are: one germicidal lamp (1849 and 2537Angstrom) having an input power of one watt per linear inch; inerting by200 standard cubic feet per inch (scfh) per foot of line width ofnitrogen; and a line speed of 23 feet per minute. An ultraviolet flux inthe range of about 10 to about 50 watts per square foot (unfocused) isdesirable.

After step (b), the coated substrate is passed through or maintained ina space essentially devoid of ultraviolet light (also referred to asdwell, dark, or black space) for a period of time sufficient for thesurface of the coating to texture. Typical time periods are about 0.5 toabout 30 seconds and preferably about 1 to about 15 seconds, but, again,the length of the space, the line speed, and the amount of texture areconsidered. In order to determine whether the texture is sufficient forthe end use, the surface is observed, both with the naked eye and underhigh magnification. In this context, texturing and shrinkage aresynonymous for it is the shrinkage at the surface of the substrate whichprovides the ultraviolet textured pattern. A typical dark space is 24inches long at 20 to 120 feet per minute line speed. It should bepointed out that the parameters of the viscosity increasing step andsteps (b) and (c) are the determinants of the ultimate texture of thecoated substrate, each complementing and/or compensating for the other,e.g., the viscosity can be increased together with the dark space toprovide an ultra-fine texture while both can be reduced to provide afine texture. The dark space atmosphere can be inserted or can be an airatmosphere.

Step (d) is the conventional curing step used in the photocure art. Thecoated substrate is exposed to ultraviolet light having wavelengths inthe range of about 1800 to about 4000 Angstroms in an inert atmospheresuch as nitrogen or in air until the coating is essentially cured. Incontradistinction to the viscosity increasing step, step (d) isirreversible. Thus, the product of step (d) is the finished product.Preferably, step (d) wavelengths are in the range of about 2000 to about4000 Angstroms. This step can be accomplished by the use of controlledor full spectrum lamps having an input power of 100 to 200 watts perlinear inch and an ultraviolet flux of about 75 to about 2500 watts persquare foot where the coating thickness is about 0.25 mil to about 10mils or even greater.

The invention is illustrated by the following examples:

EXAMPLES 1 to 38

The process is carried out in the examples in the preferred mannerdescribed above.

The apparatus used in these examples is similar to that shownschematically in FIG. 1 of U.S. Pat. No. 3,807,052, mentioned above, anddescribed therein, with two ultraviolet light modules added upstreamfrom the gas injection means. Thus, the viscosity increasing step isconnected in a first module; step (b) is conducted in a second module;step (c) is conducted in the space under the gas injection means, thisarea being a dark space (essentially devoid of ultraviolet light); andstep (d), or the curing step, in a photocure module as in '052. Thecoated substrate passes on a continuous belt underneath each module,which contains the ultraviolet lamps needed for the particular step.Since step (b) is always carried out in an inert atmosphere, the gasinjection means is set up to make this accommodation. Where air is usedin the viscosity increasing step, as is the case in these examples, avent is provided just upstream of the step (b) module to provide an exitfor both the air and the inert gas, the inert gas being used not only instep (b), but in steps (c) and (d) as well.

The coatings used are proprietary compositions and each is subjected tothe texturing test described above to determine its usefulness insubject process. The coatings are identified by the Roman numeral, whichprecedes each coating in the specification. The same apparatus is usedfor the texturing test and the Diffraction Test as is used for theexamples. Since the highest viscosities are used to obtain the ultrafinetextures, the coatings to be used at the highest viscosities aresubjected to the Diffraction Test and the maximum viscosities at whichthe coatings will pass the Diffraction Text are determined.

The apparatus is 17 feet long and 48 inches wide; the viscosityincreasing module is 24 inches long; the step (b) module is 16 incheslong; the dark space is 24 inches long; and the step (d) module is 6feet long. There are 8 inches between the viscosity increasing moduleand the step (b) module.

The viscosity increasing step is conducted in a three lamp module asdescribed above. Three spectrally controlled ultraviolet lamps are usedin the array having wavelengths in the range of 2000 to 4000 Angstroms;each delivering 30 watts per linear inch; each is provided with aprefocused relector and a Vycor filter for filtering out wavelengths inthe 2000 to 3000 Angstrom range. The lamps can be vertically adjusted todefocus, if required. The observed focal band for each lamp is about 0.5inch and the calculated ultraviolet flux is about 800 watts per squarefoot. Each lamp has an ultraviolet efficiency of about 26 percent. Note:it is preferred to use multiple lamps in the viscosity increasing stepas this provides fine control.

The line speed ranges from 47 feet per minute to 67 feet per minute.

The step (b) module has 6 VH-type germicidal ultraviolet lamps, eachhaving wavelengths at about 1849 Angstroms and 2537 Angstroms; an inputpower of one watt per linear inch; and an ultraviolet flux variable fromabout 8 to 50 watts per square foot.

The flow of nitrogen through this step (b) module is about 300 scfh(standard cubic feet per hour) per foot of line width. This same flowrate prevails in step (c) (the dark space) and the step (d) module.

The step (d) module has 6 spectrally controlled ultraviolet lamps, eachhaving wavelengths in the range of 2000 Angstroms to 4000 Angstroms; aninput power of 100 watts per linear inch; and an ultraviolet flux ofabout 150 watts per square foot.

The coatings are applied to the substrate by the screen printingtechnique using 200 mesh screens except where they are screened onto thesubstrate using 350 and 420 mesh screens as noted. All coatings have aviscosity of at least about 50 centiposes as applied and are 0.4 to 0.8mil in thickness.

The variables are set forth in Table I.

                                      TABLE I                                     __________________________________________________________________________                           No. of lamps       Line speed                                                 (viscosity                                                                            Vycor                                                                             No. of lamps                                                                         (Feet per                           Example                                                                            Coating                                                                            Substrate    increasing step)                                                                      Filters                                                                           step (b)                                                                             minute)                                                                             Result                        __________________________________________________________________________     1   VII  Lexan polymer                                                                              1       0   2      60    Fine Text.                     2   "    "            2       1   2      60    Very Fine Text.                3   "    "            3       2   2      60    Ultra-Fine Text.               4   III  "            1       0   2      60    Fine Text.                     5   "    "            1       1   3      60    Ultra-Fine Text.               6   "    "            1       1   2      60    Very Fine Text.                7   IV   "            1       0   6      60    Fine Text.                     8   "    "            2       0   6      60    Very Fine Text.                9   "    "            3       0   6      60    Ultra-Fine Text.              10   VIII Lexan polymer (350 mesh)                                                                   3       0   6      60    Ultra-Fine Text.              11   "    Lexan polymer (420 mesh)                                                                   3       0   6      60    Ultra-Fine Text.              12   VI   Lexan polymer                                                                              1       0   6      60    Fine Text.                    13   "    "            2       0   6      60    Very Fine Text.               14   "    "            3       0   6      60    Ultra-Fine Text.              15   IX   "            0       0   6      60    Coarse Text. (Std.)           16   "    "            2       0   6      60    Ultra-Fine Text.              17   "    "            3       0   2      60    Ultra-Fine Text.              18   I & IX                                                                             "            3       0   1      66    Ultra-Fine Text.              19   "    "            3       0   1      71    Very Fine Text.               20   I    "            0       0   2      60    Coarse Text. (Std.)           21   "    "            0       0   6      60    Coarse Text. (Std.)           22   "    "            1       0   6      60    Fine Text.                    23   "    "            2       0   6      60    Fine Text.                    24   "    "            3       0   6      60    Very Fine Text.               25   "    "            3       0   6      47    Ultra-Fine Text.              26   "    "            3       0   6      57    Ultra-Fine Text.              27   "    "            3       0   6      67    Very Fine Text.               28   "    "            3       0   2      67    Fine Text.                    29   V    Lexan polymer                                                                              3       0   1      58    Ultra-Fine Text.              30   "    with black   3       0   1      66    Ultra-Fine Text.              31   "    back-up      2       0   1      66    Fine Text.                    32   XIV  Lexan polymer                                                                              3       0   6      60    Ultra-Fine Text.              33   XIII "            3       0   6      60    Ultra-Fine Text.              34   I    Litho stock  0       0   0      60    High Gloss Finish             35   "    "            0       0   2      60    Coarse Text. (Std.)           36   "    "            3       0   2      60    Very Fine Differential                                                        Text.                         37   "    "            0       0   6      60    Coarse Text. (Std.)           38   "    "            3       0   4      60    Ultra-Fine Differential                                                       Text.                         __________________________________________________________________________     Notes:                                                                        Coarse Text. (Std.)--Low Gloss rough textured surface where any               imperfections readily may show                                                Fine Text.--Low Gloss texture, imperfection free surface                      Very Fine Text.--Medium Gloss texture, imperfection free surface              Ultra-Fine text.--Semi Gloss texture, imperfection free surface               Differential Text.--Texture over dark on nonreflective areas and gloss        over light or reflective areas                                           

EXAMPLES 39 to 44

Example 1 is repeated except that the module for the viscosityincreasing step is changed to one Vycor envelope ultraviolet lamp thathas an ultraviolet output of 3000 to 4000 Angstroms and an input powerof 64 watts per linear inch. All test applications are made with anumber 60 wire wound rod draw down bar. The coating thicknesses areabout 4 mils plus or minus 0.5 mil. The substrate is conventionalvinyl-asbestos floor tile. The line speed ranges from 20 feet per minuteto 120 feet per minute.

The variables are set forth in Table II. It is noted that in allexamples the texture is insensitive to plus or minus 0.5 mil variationin coating thickness.

EXAMPLES 45 to 50

Example 39 is repeated. The coating used is number II. One ultravioletlamp is used in the step (b) module and one in the step (d) module. Thelamps are the same type of lamp that is used in the step (b) module ofexample 39.

The variables are set forth in Table III. A smooth surface with uniformlow gloss level across all areas is obtained.

                  TABLE II                                                        ______________________________________                                                        No.      Line speed                                                           of Lamps (feet per                                            Example                                                                              Coating  step (b) minute) Results                                      ______________________________________                                        39     III      2        20      Fine Text.                                   40     III      6        20      Very Fine Text.                              41     I        2        70      Very Fine Text.                              42     I        6        70      Ultra-Fine Text.                             43     I        2        120     Fine Text.                                   44     I        6        120     Very Fine Text.                              ______________________________________                                    

                  TABLE III                                                       ______________________________________                                                            Line Speed                                                        Coating Thick-                                                                            (feet per                                                 Example ness (mils) minute)    Results                                        ______________________________________                                        45       10         75         Ultra-Fine Text.                               46      5           100        Very Fine Text.                                47      4           125        Fine Text.                                     48      6           125        Fine Text.                                     49      8           125        Fine Text.                                     50      6 to 9      100        Very Fine Text.                                ______________________________________                                    

I claim:
 1. In a process for providing a textured or woven coating on asubstrate, which coating has a thickness of about 0.1 mil to about 10mils, comprising the following steps:(a) applying a coating, which iscurable with ultraviolet light, to the substrate, said coating having aviscosity, as applied, of at least about 50 centipoises; (b) exposingthe coated substrate to ultraviolet light having wavelengths in therange of about 1800 Angstroms to about 2750 Angstroms in an inertatmosphere for a period of time sufficient to initiate texturing at thesurface of the coating; (c) maintaining the coated substrate from step(b) in a space essentially devoid of ultraviolet light for a period oftime sufficient for the surface of the coating to texture; and (d)exposing the coated substrate from step (c) to ultraviolet light havingwavelengths in the range of about 1800 Angstroms to about 4000 Angstromsin an inert atmosphere or air until the coating is essentially cured,the improvement comprising, after step (a) and prior to step (b),increasing the viscosity of the coating by exposing the coating toultraviolet light, said viscosity being increased to a viscosity nohigher than that at which the coating is capable of being textured insteps (b) and (c), above.
 2. The process defined in claim 1 wherein theultraviolet light used in increasing the viscosity has wavelengths inthe range of about 1800 to about 4000 Angstroms.
 3. The process definedin claim 2 wherein the viscosity of the coating is increased at leastabout 25 percent over its applied viscosity.